Vacuum pump

ABSTRACT

A vacuum pump includes shaft, two spaced from each other, dynamic gas bearings for supporting the shaft for rotation, and a pumping system arranged on the shaft between the two gas bearings and having two pumping sections which are so formed that compressed gas from each section is delivered in a direction of a gas bearing adjacent to this pumping section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum pump having a shaft supported for rotation by two radial bearings, and a pumping system arranged on the shaft.

2. Description of the Prior Art

In many technical fields, the production of a high vacuum with pressures lower than 10⁻⁴ mbar is of great importance. There is an increasing need in compact vacuum pumps capable of producing such pressures. In the state of the art, however, often, pumping stations are used. In the pumping stations, several separate pumps, which are adapted to particular pressure regions, are combined. Recently, vacuum pumps dischargeable into atmosphere have been developed. In these pumps, several pumping principles are combined. E.g., the German Publication DE 199 30 952 A1 proposes to combine Holweck pumping stages with peripheral stages. However, the proposed construction, because of its rather high costs, is only attractive for class of pumps having a suction capacity above 20 m³/hr.

Accordingly, an object of the present invention is a vacuum pump capable to bridge the entire pressure region from atmospheric pressure and up to a high vacuum of 10⁻⁴ mbar and smaller.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a vacuum pump including spaced from each other, first and second dynamic gas bearings for supporting the shaft for rotation, and a pumping system arranged on the shaft between the first and second gas bearings and having two pumping sections which are so formed that a compressed gas from each of the two pumping sections is delivered in a direction of a gas bearing adjacent to a respective pumping section.

The provision of gas bearings permits to simplify the pump construction. Gas bearings do not require any organic lubricant so that a lubricant circuit with a lubricant pump can be eliminated, and no contamination of a recipient and the pumped gas can occur. Gas bearings are subjected to very little wear, which permits to achieve an extended service life of the pump, together with substantially reduced maintenance costs. The construction of the pump is simplified due to a favorable gas guidance.

The favorable gas guidance is achieved by providing, in the pump system, pumping sections that pump gas in directions of respective gas bearings. Therefore, sealing means between the gas bearings and the pumping system can be eliminated. A further advantage of the gas guidance according to the present invention consists in that the axial forces, which are produced in each pumping section by pressure difference between its gas inlet and gas outlet, are compensated. Therefore, overall, no axial forces acting on the shaft are produced by the pumping system. As a result of elimination of certain components and of the favorable gas guidance, a very compact vacuum pump is formed.

The gas delivery is further improved by arranging the respective pumping sections and the gas bearing adjacent thereto so that at least a portion of an operational gas of the gas bearing and gas expelled from the respective pumping section are combined at a point and flow together to a pump outlet. Such an arrangement further contributes to the compactness of the inventive vacuum pump.

According to further development of the present invention, at least one of the two pumping sections includes a Holweck pumping stage. Holweck pumping stages have spiral-shaped channels. They can be formed in single manufacturing step together with structures necessary for gas bearings.

In addition, a Holweck pumping stage requires only few components, namely, channels formed in the shaft surface, and an opposite smooth cylindrical surface. Thereby, the vacuum pump is not only a low-cost pump but is also a very compact pump.

According to a still further development of the present invention, the Holweck stage includes, in addition to the channels formed in the shaft surface, oppositely directed channels provided on the stator. This increases the suction capacity, in particular in a pressure region adjacent to atmosphere. Therefore, less constructional space is needed for an increased suction capacity. This additionally contributes to the compactness of the inventive vacuum pump.

According to a still further development of the present invention, the suction capacity can be increased by providing, in a vacuum pump, a further pumping system. Advantageously, the further pumping system also has a Holweck pumping stage. This one is formed by a hub connected with one end of the shaft, and a cylinder connected with the hub.

According to a yet further development of the present invention, a back-up bearing is provided at the shaft ends. The back-up bearings can be formed as slide bearings. The back-up bearings permit to form a robust vacuum pump as they can withstand axial forces acting on the shaft.

According to the present invention, the shaft material substantially consists of silicon carbide. This material combines the compatibility with the gas bearings with stability of the vacuum pump in different applications.

According to the present invention, the rotor and the stator of the drive motor of the vacuum pump are so formed that they provide for an axial centering and, simultaneously, a rapid rotation of the shaft. This permits to eliminate the need for axial bearings, which further contributes to cost-effectiveness and compactness of the inventive vacuum pump.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

The drawings show:

FIG. 1 a cross-sectional view of vacuum pump according to the present invention; and

FIG. 2 a cross-sectional view of a section of a vacuum pump according to a further embodiment of the present invention with a pumping system different from that of the vacuum pump shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vacuum pump according to the present invention, which is shown in FIG. 1, has a housing 1 having a gas inlet 7 and a gas outlet 8. Inside the housing 1, there is arranged a cylinder 5 in which a shaft 2 is rotatably supported. At its opposite ends, the shaft is supported by two gas bearings 30 and 40, respectively.

The first gas bearing 30 includes a gas inlet 31, a shaft-side bearing structure 32 and a bearing gas outlet 34. The bearing structure 32 forms a bearing section 33 extending in the shaft axial direction.

The second gas bearing 40 includes a gas inlet 41, a shaft-side bearing structure 42 and a bearing gas outlet 44. The bearing structure 42 forms a bearing section 43 extending in the shaft axial direction.

The bearing structures 32 and 42 include recesses formed in the surface of the shaft 2.

In the embodiment shown in FIG. 1, each of the gas bearing outlets 34 and 44 is provided with two openings located, respectively, at opposite ends of the respective bearing section 32, 42. Further, though in FIG. 1, only one gas inlet 31, 41 is shown, respectively, as a rule a plurality of such inlets is provided in each bearing and which are distributed over the shaft circumference. The cylinder 5 forms the stator of both gas bearings 30 and 40, so that a gas film is formed between the shaft-side bearing structures 32 and 42, respectively, and the cylinder 5, with the shaft 2 being supported by the gas films. The necessary bearing gas can be produced by a compressor 11 or, when the bearing load permits, can be taken directly from the atmosphere. In the latter case, the gas inlets 31, 41 communicate directly with the atmosphere.

Alternatively, a compressed air from an on-site available, compressed air conduit can be used.

The shaft 2 has, at one of its ends, a shaft journal 29 on which permanent magnets 9 are mounted. The permanent magnets 9 form a rotor of a drive motor and cooperate with electrical coils 10 to provide for a rapid rotation of the shaft 2 about its longitudinal axis. The electrical coils 10 form a stator of the drive motor. The motor rotor and the motor stator are so formed that they stabilize the shaft in the direction of its longitudinal axis. This is achieved, e.g., by action of the attraction forces of the stator iron core on the permanent magnets. At the shaft end, a back-up bearing is provided. In the embodiment shown in FIG. 1, the back-up bearing is formed as a slide bearing 14 that includes, on its shaft side, a spherical surface and, on its housing side, a tribologically suitable counter-surface. If large axial forces are expected, for an additional stabilization, permanent magnet rings can be provided in the axial direction, namely, a shaft-side bearing ring 26 and a stator-side bearing ring 27. The two bearing rings 26, 27 form an axial permanent magnet bearing 25.

Electronics 20 is arranged in an electronic housing 21. The electronics 20 is connected with the electrical coils 10. If the compressor 11 is used for production of the bearing gas, the compressor control conductor 22 of the compressor 11 is connected with the pump electronics 20 that controls the operation of the compressor 11, in particular its parameters such as actuation, deactuation, pressure level, and a feed amount.

On the shaft 2, between the bearing sections 33 and 43, a pumping system 6 is arranged. The pumping system 6 is formed as a double-flow system and has a first pumping section 61 and a second pumping section 62. Each of the pumping sections 61, 62 starts in a region of the gas inlet 7, and the compressed gas flows in the direction of the gas bearing adjacent thereto, as shown by a straight arrows. From the bearing sections, at least a portion of the bearing gas is released in the direction of the pumping system. The gas flows are combined at a location 13 between the first gas bearing 30 and the first pumping section 61 or at a location 13′ between the second gas bearing 40 and the second pumping section 62 and together are fed to the pump or housing outlet 8. This permits to obtain a very compact structure as a result of a simple gas flow circuit.

Both pumping sections achieve the same pressure ratios between their respective inlets and outlets. Advantageously, Holweck structures are provided in the pumping sections. In addition, in the shaft surface, there are formed spiral-shaped channels 63 which circumscribe the shaft 2 and cooperate with an inner surface of the cylinder 5 that acts as a pump stator. If the inner surface is smooth, a pump based on the working principle according to Holweck, is formed. This is not only favorable for the pressure region from the vacuum technical point of view but also allows advantageously to produce the shaft, together with the shaft-side bearing structures, in a single operational step. According to a further modification, on the inner surface of the cylinder 5, channels 64 are provided. The channels 64 extend over a portion of the axial length of the pumping sections 61 and 62, preferably, in the portion adjacent to the respective gas bearings 30, 40. The channels 64 are to be formed so that they run opposite to the channels 63 on the shaft 2, the pump rotor. The stator-side channels increase the suction capacity.

The shaft 2 is formed as one piece at least in the region of the bearing sections 33, 43 and the pumping sections 61, 62. The cylinder 5 is likewise formed as one piece, at least in its region extending over the bearing sections 33, 43 and the pumping section 61, 62. Thereby, the bearing points are aligned, so that extremely small gaps are formed in the bearings and in the pumping system. This improves the performance characteristics of these components, so that the necessary constructional length is reduced, making the vacuum pump more compact.

Because this vacuum pump is dynamically sealed, in a non-actuated condition, the gas can flow therethrough. Therefore, the use of a safety valve 12 is advantageous. The valve 12 is advantageously provided in the gas inlet 7 of the vacuum pump and is connected by the valve control conductor 23 with the electronics 20. The control electronics 20 turns on the open condition of the safety valve 12.

FIG. 2 shows a section of a further embodiment of the inventive vacuum pump designated as a box K. In comparison with the embodiment shown in FIG. 1, the vacuum pump shown in FIG. 2 includes a further pumping system 100 located upstream of the pumping system 6. Here, in the housing of the vacuum pump, a Holweck stator 103 is provided. The stator 103 has, in its cylindrical inner surface, a thread-shaped channel. The pitch sections of the channel are separated from each other by webs 105. A smooth cylinder 102 cooperates with the thread-shaped channel, whereby a pumping action is produced. The cylinder 102 is connected with a hub 101. Advantageously, the cylinder 102 is formed of a light material, in particular of fiber-reinforced carbon. The hub 101 is secured on an end of the shaft, so that the hub 101 and the cylinder 102 rotate with the same speed as the shaft 2 (see FIG. 1). There are further provided a slide bearing 14 and the inlet 7, with a safety valve 12. Gas flows through the gas inlet 7 and into the further pumping system 100, as shown by the first arrow, and is compressed there by respective portions of cooperating parts of the Holweck stator and the cylinder 102. Then, the gas flows into the first pumping system 6, as shown by the second arrow, and is further compressed there. The first pumping system 6 is shown only partially, with only pumping section 62 being shown completely. Likewise, only the shaft-side bearing structure 42 of the second bearing 40 is shown. From the bearing structure 42, the bearing gas at atmospheric pressure exits in the direction of the hub 101. The exiting bearing gas should not be allowed to reach the inner surface of the cylinder 102 and along in the inlet of the first pumping system 6. In order to prevent the bearing gas from reaching the inlet of the first pumping system 6, a sealing section 106 is provided between the bearing structure 42 and the hub 101. The sealing section 106 is formed by arranging on the shaft a pumping structure, as in the first pumping system, and which cooperates with the cylinder 5 to produce a pressure difference. The pumping structure of the sealing section is so formed that the pressure ratio between the side of the pumping structure adjacent to the bearing structure 42 and the side of the pumping structure adjacent to the hub 101 corresponds to the pressure ratio produced by the pumping section 62. However, the suction capacity of the pumping structure of the sealing section 106 can be noticeably smaller, as a smaller amount of bearing gas than that entering through the inlet 7 is used. The further pumping system 100 can also be formed as a double-flow system.

Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. A vacuum pump, comprising a shaft; spaced from each other, first and second dynamic gas bearings for supporting the shaft for rotation; and a pumping system arranged on the shaft between the first and second gas bearings and having two pumping sections which are so formed that a compressed gas from each of the two pumping sections is delivered in a direction of a gas bearing adjacent to a respective pumping section.
 2. A vacuum pump according to claim 1, wherein each of the pumping sections and the gas bearing adjacent thereto are so arranged that at least a portion of an operational gas of the gas bearing and gas expelled from the respective pumping section are combined at a point and flow together to a pump outlet.
 3. A vacuum pump according to claim 1, wherein at least one of the two pumping sections includes a Holweck pumping stage
 4. A vacuum pump according to claim 3, wherein both rotor and stator of the Holweck stage each has channels extending in opposite directions.
 5. A vacuum pump according to claim 1, further comprising a further pumping system.
 6. A vacuum pump according to claim 5, wherein the further pumping system includes a hub connected with one end of the shaft, and a cylinder connected with the hub.
 7. A vacuum pump according to claim 1, further comprising a back-up bearing provided at one end of the shaft.
 8. A vacuum pump according to claim 7, wherein the back-up bearing is formed as a slide bearing.
 9. A vacuum pump according to claim 1, wherein a shaft material substantially consists of silicon carbide.
 10. A vacuum pump according to claim 1, further comprising a shaft driving motor having stator and rotor thereof so formed that an axial centering and simultaneously a rapid rotation of the shaft are provided for. 